[gmx-developers] warning Emulating FMA instructions - this is probably not what you want!

[Szilárd Páll]

On Thu, Oct 18, 2012 at 1:24 PM, Berk Hess <hess at kth.se> wrote:

>  It seems that for many other packages it does work, so we might want to
> comply with that.
>
> But here we seem to have another issue: -mfma4 was not added automatically.
> CMakeLists.txt never checks for this. Did Erik simply forget to do so?
>

I assume so, I don't know of any other reason for -mfma4 to be omitted.
Here's the very detailed bug report, just in case if somebody wants to
refer to it when fixing it ;)
http://redmine.gromacs.org/issues/1023

Cheers,
Szilárd


>
> Cheers,
>
> Berk
>
>
> On 10/18/2012 01:01 PM, Szilárd Páll wrote:
>
> That's correct. The point I was trying to make is that we might end up
> hearing about this issue in the future if people use CFLAGS just by
> routine. I fact, I'm not even sure that cmake is not supposed to pick up
> CLAGS as well and it's some later cmake pass rewriting compiler options is
> that the current code is trying to overcome, but it ends up loosing some
> options when CFLAGS is set.
>
>  Any comments? Should CFLAGS work?
>
> --
> Szilárd
>
>
> On Thu, Oct 18, 2012 at 9:43 AM, Jochen Hub <jhub at gwdg.de> wrote:
>
>> Following Szilard, I tried to use
>>
>> cmake -DCMAKE_C_FLAGS=-mfma4 ...
>>
>> instead of export CFLAGS=-mfma4 to add the -mfma4 flag. Now, the only
>> difference in CMakeCache.txt is
>>
>> < CMAKE_C_FLAGS:STRING='-mavx  -Wall -Wno-unused -Wunused-value  '
>> ---
>> > CMAKE_C_FLAGS:STRING=-mavx  -Wall -Wno-unused -Wunused-value  -mfma4
>>
>> which is just what I wanted, right? (and the warning on emulating FMA
>> instructions does not appear any more).
>>
>> Jochen
>>
>>
>> Am 10/17/12 11:28 PM, schrieb Szilárd Páll:
>>
>>>
>>> That way of calling CMake triggers an interesting bug in the option
>>> generator and CFLAGS will essentially override part of the
>>> auto-generated compiler options. Diff of relevant lines in
>>> CMakeCache.txt are below, the only difference is that the second file
>>> ("+" in the diff) was generated by running "CFLAGS=-march=native
>>> cmake...":
>>>
>>>   //Flags used by the compiler during all build types
>>> -CMAKE_C_FLAGS:STRING='-msse2  -Wall -Wno-unused -Wunused-value  '
>>> +CMAKE_C_FLAGS:STRING='-msse2  -march=native '
>>>   //Flags used by the compiler during debug builds.
>>> -CMAKE_C_FLAGS_DEBUG:STRING=-fno-inline  -g
>>> +CMAKE_C_FLAGS_DEBUG:STRING=-g
>>> -//Flags used by the compiler during release builds.
>>> -CMAKE_C_FLAGS_RELEASE:STRING=-fomit-frame-pointer -funroll-all-loops
>>> -fexcess-precision=fast  -O3 -DNDEBUG
>>> +//Flags used by the compiler during release builds (/MD /Ob1 /Oi
>>> +// /Ot /Oy /Gs will produce slightly less optimized but smaller
>>> +// files).
>>> +CMAKE_C_FLAGS_RELEASE:STRING=-O3 -DNDEBUG
>>>
>>> As this messes with "considered to be best basic set of options", we
>>> could state that CFLAGS should not be used, but it might be a better
>>> alternative to make the configuration prepend the CFLAG to the
>>> CMAKE_C_FLAGS and keep our generated set of flags as well.
>>>
>>> I'm not sure which options is best. Thoughts?
>>>
>>> --
>>> Szilárd
>>>
>>>
>>>
>
> --
> gmx-developers mailing list
> gmx-developers at gromacs.org
> http://lists.gromacs.org/mailman/listinfo/gmx-developers
> Please don't post (un)subscribe requests to the list. Use the
> www interface or send it to gmx-developers-request at gromacs.org.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-developers/attachments/20121018/610cf939/attachment.html>